The long-term goal of the proposed studies is to define the role of ubiquitin-mediated proteolysis (UMP) in cell fate determination during dorsoventral patterning. UMP by the 26S proteosome has been shown to play critical roles in regulating cellular activities. While broadly implicated in cell fate determination during early embryogenesis, currently little is known about the exact role and regulation of UMP in dorsoventral patterning, which forms the foundation for the generation of germ layers and ontogenesis of tissues and organs. Previous studies have shown that both -catenin from the dorsal signaling center and Xom from the ventral signaling center are controlled by UMP. It is well appreciated that during early embryogenesis, ventral (Xom) signaling antagonizes dorsal (-catenin) signaling; nevertheless, the intrinsic function of UMP in dorsoventral signaling is not clear. The goal of this application is to define the function of UMP in balancing dorsal and ventral signals. The research derives from the principal investigator's preliminary studies, which allowed him to formulate the hypothesis that Xom antagonizes dorsal signaling through GSK-mediated proteolysis of -catenin. Using combined biochemical and genetic approaches and a Xenopus model, the investigators propose to further test their hypothesis through the following two specific aims. Aim 1 will determine the mechanisms of Xom-induced proteolysis of -catenin in vitro by defining the involvement of GSK3 kinase and Ser33/37 phosphorylation. In addition they will identify the critical domain of Xom required for inducing proteolysis of -catenin. Aim 2 will define the effects of Xom on UMP of -catenin in vivo by determining the effects of Xom and GSK3 in the temporal and spatial expression pattern of the -catenin protein and mRNA during early embryogenesis. The results of the proposed studies will introduce a new paradigm underlying the formation of dorsal-ventral asymmetry, and are expected to pave the way for understanding stem cell function and future management of congenital malformations and neoplastic diseases. PROJECT NARRATIVE: Molecular mechanisms controlling the formation of dorsal-ventral axis formation represent a fundamental challenge of early embryogenesis. The proposed studies will focus on the role of ubiquitin-mediated proteolysis in dorsoventral patterning formation. The results of these studies will be broadly implicated in preventing congenital malformation, regulating stem cell function, as well as managing neoplastic diseases.